Method of making a prosthetic socket component

ABSTRACT

A method of forming a socket for connecting a prosthesis to an amputated extremity including forming a molded cast into which an amputated extremity conforms, the molded cast having a closed distal end for positioning adjacent one end of the amputated extremity and an open proximal end for surrounding the amputated extremity, forming a vacuum assembly by connecting an attachment device for receiving a vacuum tube to the distal end of the mold cast and attaching a first end of the vacuum tube to the attachment device. Subsequently, wrapping a formable plastic layer around a portion of the vacuum tube, the attachment device and at least the distal end of the molded socket. The plastic layer is sealed around the vacuum tube and at least the distal end of the molded cast such that trapped air between the plastic layer and the vacuum assembly can be drawn through the vacuum tube, thus conforming the formal plastic layer to at least the distal end of mold cast and the attachment device. Once formed, excess portions of the foldable plastic layer are trimmed with the vacuum tube being removed leaving the attachment means secured in place by the formable plastic layer.

This is a Divisional application of Ser. No. 08/637,041, filed Apr. 24,1996, now U.S. Pat. No. 5,711,973.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to a method and apparatus formaking a prosthetic socket for an amputated limb and specifically aprosthetic socket. More particularly, the present invention relates to amethod and apparatus for manufacturing a prosthetic socket of plasticmaterial using a vacuum-forming technique which allows prostheticcomponents to become an integral part of the socket.

2. Background Art

Often, a prosthesis is required to assist in restoring an amputee'sability to accomplish many of life's daily tasks. In the case of lowerextremity amputations such as the loss of a leg, the prosthesis allowsthe amputee to stand, walk and run by providing a mechanical extensionto the residual limb or stump. Such a prosthesis may comprise anartificial foot connected to an artificial limb shaft with acustom-fitted socket and an elastic sleeve at one end which fits overthe residual limb for securing the socket to the residual limb. One ofthe most important aspects of these prosthesis is strength socketdesign, the socket being the load-bearing interface between the residuallimb and the mechanical support system.

Because each socket must be custom-fitted to the individual patient,socket design and fabrication have been heretofore quite expensive andtime-consuming. One technique commonly used to make prosthetic socketshas been to drape a sheet of heated plastic over a positive cast of theresidual limb, manually forming the plastic to conform to the contoursof the cast. This technique, known as "drape-forming" usually requirestwo persons and a large degree of manual skill. Further, it oftenresults in significant amounts of wasted plastic and nonuniform forming.

Another technique previously disclosed has been to provide a generallyconical, hollow socket preform of memory plastic material which is thenplaced over a positive cast of the residual limb, the combination beingplaced in an oven and heated sufficiently to induce shrinkage of thepreform onto the cast surface to create a semi-finished socket. Thistechnique, known as "shrink-forming", takes advantage of thecharacteristics of such memory plastic materials, in particular theirtendency to return to their original shape when reheated.

Although shrink-forming offers a more efficient, less labor- andskill-intensive method of socket fabrication than drape-forming, thebasic method as described above suffers from several problems. First,the preform may develop imperfections or even perforations duringheating at the points of initial contact with the positive cast. This isdue to the temperature differential between the cast and the preformduring heating, with the cast acting as a heat sink at these points ofinitial contact. Second, the conventional convection-type ovenspresently used in shrink-forming result in nonuniform heating of thepreform which in turn results in nonuniform shrinkage of the preformover the cast. Finally, the degree of shrinkage of presently availablepreforms is less than optimal for these purposes, although thisdeficiency may be somewhat compensated for by applying a vacuum to thepreform/cast interface to help conform the preform to the contours ofthe cast.

It is believed that the root of the last-mentioned problem lies not somuch with the shrink-forming technique but rather with the preformitself. A particularly advantageous method of producing the socketpreform utilizes blowmolding, offering fewer steps than other techniquessuch as injection molding. Blowmolding in such an application involvesextruding heated plastic through a mandrel and die to form a parison ortube, enclosing the parison within a mold, and injecting air into theparison until it expands to conform to the contours of the inner cavityof the mold. The use of standard blowmolding techniques, however, doesnot produce a preform product with optimal shrinkage characteristics.Further, standard blowmolding molds often produce an undesirable raisedportion or rib on the inner surface of the preform at its upper end.Because of its location, this rub is difficult to remove and oftencreates a non-uniform area in the final product. Finally, conventionalmolds also suffer from parison severing at the upper mold interfaceduring blowmolding of plastics that have a high melt flow index.

In order to avoid the heat-sinking effects and the non-uniform shrinkageof the preform over the cast associated with the prior art, U.S. Pat.No. 5,376,129 to Faulkner et al. discloses a heat and vacuum-formingtechnique for forming a preform over the exterior surface of a cast.This method first preheats the cast to minimize the temperaturedifferential between the cast and the preform, and then the preform isplaced over the cast and heated in the oven to shrink the preform overthe exterior surface of the cast. A partial vacuum is also applied tothe inner chamber of the cast to further conform the preform with theexterior surface of the cast. This method, however, requires anadditional step of drilling holes through the cast to allow air totravel from the exterior surface of the cast toward the vacuum formed inthe inner chamber of the cast. Furthermore, this method involves acomplicated process of heating the cast and preform while simultaneouslyapplying a vacuum to the assembly.

A further problem existing in the presently available socket formingtechnology relates to the device used for attaching the socket to anartificial limb shaft. The present socket forming techniques require theadditional time-consuming step of removing excess plastic from aroundthe attachment device after the preform is shrunk onto the cast. Thisstep adds additional expense to the already costly prosthesis since itis imperative to provide a clean connection between the attachmentdevice and the artificial shaft in order to provide adequate support forthe artificial limb.

Accordingly, there is clearly a need for a method and apparatus forreliably producing a prosthetic socket having an attachment device whichis free from plastic material, wherein an additional step of removingthe plastic material from the attachment device is not required afterthe prosthetic socket is formed. It is further desirable to provide amethod of forming a prosthetic socket which avoids the problem ofnonuniform shrinkage of the preform over the cast and makes for astronger attachment point for components.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to overcome theaforementioned shortcomings associated with the prior art.

Another object of the present invention is to provide a method andapparatus for forming a prosthetic socket having an attachment devicewhich does not require the procedure of removing plastic material fromthe attachment device in order to provide a clean surface to which anartificial limb may be attached.

Yet another object of the present invention is to provide a method andapparatus for forming a prosthetic socket having uniform shrinkage of aplastic material over the cast for the residual limb.

A further object of the present invention is to provide a method andapparatus for forming a prosthetic socket having a more stableconnection to an artificial limb.

These as well as additional objects and advantages of the presentinvention are achieved by providing a vacuum tube assembly for vacuumsealing a layer of plastic material onto a molded cast to form aprosthetic socket. The vacuum tube assembly includes a cylindrical shaftfor providing an air path between the molded cast and a vacuum suctiondevice. The cylindrical shaft includes a connection device attached toone end of the cylindrical shaft, wherein the connection device is usedfor affixing the vacuum tube assembly to an attachment device on theprosthetic socket. The attachment device is formed within the prostheticsocket and is affixed to the molded cast, wherein the attachment deviceis the component which connects the prosthetic socket to an artificiallimb shaft. A reciprocating cover is also provided on one end of thecylindrical shaft for covering the connection device, so that thereciprocating cover abuts the prosthetic socket when the connectiondevice is affixed to the attachment device. The reciprocating cover isspring-loaded against the cylindrical shaft so that the spring exerts aforce against the reciprocating cover toward the prosthetic socket,wherein a force must be exerted against the cover sufficient enough toovercome the spring-load in order to allow access to the connectiondevice.

These as well as additional advantages of the present invention willbecome apparent from the following description of the invention withreference to the several figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the preferred embodiment of the presentinvention illustrating the vacuum tube assembly and prosthetic socketprior to the formation of the plastic layer thereon.

FIG. 2 is a sectional side view of the vacuum tube assembly inaccordance with the preferred embodiment of the present invention.

FIG. 3 is a sectional side view of the vacuum tube assembly connected tothe attachment device in accordance with the preferred embodiment of thepresent invention.

FIG. 4 is a perspective view of the prosthetic socket and vacuum tubeassembly illustrating the plastic layer being wrapped therearound.

FIG. 5 is a perspective view of the prosthetic socket and vacuum tubeassembly having the plastic layer formed therearound.

FIG. 6 is a sectional side view of the prosthetic socket in accordancewith the preferred embodiment of the present invention.

FIG. 7 is a perspective view of the prosthetic socket in accordance withthe preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a perspective view illustrates a vacuum tubeassembly 2 and a molded cast 4 of an amputated limb in accordance withthe preferred embodiment of the present invention. Typically, in orderto attach an artificial limb to an amputated limb, a molded cast 4 ofthe amputated limb must be formed to provide an intermediate connectingstructure between the amputated limb and the artificial limb. A mold ofthe amputated limb is first created to conform to the shape of theamputated limb. Next, the amputated limb cast 4 is fabricated by placinga heated plastic material around the mold so that the plastic materialembraces the same shape as the amputated limb. Therefore, the cast 4 mayfittingly receive the amputated limb to provide a more comfortablesupport for the person wearing the cast 4.

In order to connect the cast 4 to an artificial limb, an attachmentdevice 6 is affixed to the distal end 8 of the cast 4 to allow theconnection of an artificial limb thereto. The attachment device 6includes a mounting plate 10, wherein a tapered projection 12 extendsfrom the lower surface of the mounting plate 10. The tapered projection12 is the portion of attachment device 6 to which the artificial limb isattached. In the preferred embodiment of the present invention, thetapered projection 12 is integrally formed with mounting plate 10 sothat the tapered projection 12 may withstand the forces exerted betweenthe weight of the person wearing the cast 4 and the artificial limb.Furthermore, a metallic substance is preferably used in manufacturingthe mounting plate 10 and tapered projection 12 in order to provide thenecessary strength and durability of the tapered projection in view ofthe above-described forces exerted on the attachment device 6. However,it is understood by those skilled in the art that the tapered projection12 may be formed separately from the mounting plate 10 as long as theprojection 12 is securely fastened to the mounting plate 10. Further,while a metallic substance has been described as the preferablecomposition of the tapered projection 12 and mounting plate 10, anysubstance which can withstand the forces described above and hereinaftercan be utilized in conjunction with the preferred embodiment of thepresent invention.

The attachment device 6 also includes a foam material 14 located on theupper surface of the mounting plate 10 which allows the mounting plate10 to be attached to the cast 4. The foam material 14 may be affixed tothe mounting plate 10 by any suitable adhesive. Similarly, the foammaterial 14 is affixed to the distal end 8 of the cast 4 (or suitableinner liner) using a suitable adhesive, whereby the foam material 14provides a tackier surface to adhere to the cast 4 than the surface ofmounting plate 10 would provide. The upper portion of the foam material14 is further shaped to have the same contour as the distal end 8 of thecast 4 in order to provide a better contacting surface between the foammaterial 14 and the cast 4. The foam material 14 is comprised of alightweight foam substance in order to minimize the weight of theattachment device 6, yet firm enough not to distort because of heat andvacuum pressure. The adhesive affixing the attachment device 6 to thecast 4 does not have to form a permanent bond between the two surfaces,since this is only a preliminary step of attaching the attachment deviceto the cast 4. A process of overlaying a plastic material over the cast4 and attachment device 6 is subsequently performed for permanentlyaffixing the attachment device 6 to the cast 4 thereby forming aprosthetic socket, described in further detail hereinbelow.

The preferred method of forming the plastic overlayer on the cast 4 andattachment device 6 utilizes a vacuum tube assembly 2 illustrated inFIG. 1, and in greater detail in a cross-section view in FIGS. 2 and 3.The vacuum tube assembly 2 enables a prosthetic socket to be formedwhich does not require a procedure for removing excess plastic materialfrom the attachment device 6 after formation is complete.

The vacuum tube assembly 2 includes a cylindrical shaft 16 having acentral passage 18 extending from one end 20 of the shaft 16 to theother end 22. The central passage 18 provides a pathway for air flowbetween the two ends, wherein a vacuum suction device is attachable toend 20 while the attachment device 6 is attachable to end 22. Therefore,the vacuum tube assembly 2 will pull air from the end 22 of thecylindrical shaft 16 through central passage 18 and exit end 20. Aconnection device 24 is affixed to the end 22 of cylindrical shaft 16for attaching the shaft 16 to the tapered projection 12 of mountingplate 10. The connection device 24 is of generally the same shape asshaft 16, having a passage 26 extending through its center for allowinggaseous communication between the central passage 18 and the airsurrounding tapered projection 12. A plurality of screws 28 are alsothreadingly engaged in the connection device 24, whereby the screws 28extend through apertures 32 in the connection device 24. The screws 28may be tightened to abut tapered projection 12 into order to secure theconnection device 24 to the tapered projection 12, and the outwardtapering of projection 12 prevents the connection device 24 fromdisengaging with the projection 12 without the screws 28 being loosened.In the preferred embodiment, four screws 28 are utilized in theconnection device 24 with the screws being positioned equidistant fromone another around the perimeter of the connection device 24. While theconnection device 24 and cylindrical shaft 16 are described as separatecomponents in the preferred embodiment of the present invention, it isunderstood that the connection device 24 and cylindrical shaft 16 couldbe integrally formed in a unitary construction.

The vacuum tube assembly 2 also includes a cylindrical outer sleeve 30which surrounds the outer surface of the end 22 of the cylindrical shaft16, and further extends beyond the end 22 to additionally coverconnection device 24. The sleeve 30 is open at both ends to allow thesleeve to reciprocate about the surface of cylindrical shaft 16, andthis open end configuration allows air to travel through the sleeve 30and into central passage 18. Additionally provided on the outer surfaceof cylindrical shaft 16 are a pair of cylindrical collars 34 and 36.Collar 36 is affixed to shaft 16 in a manner such that the collar 36remains stationary with respect to the shaft 16. In the preferredembodiment, the collar 36 includes an inwardly directed screw which maybe adjusted to frictionally engage the shaft 16 in order to secure thecollar 36 to the shaft 16. By affixing the collar 36 to the shaft 16 inthis manner, the collar 36 may be relocated from one stationary positionto another stationary position as desired. However, the collar 36 may beaffixed to the shaft 16 by other similar means or may be permanentlyattached to the shaft 16. The second collar 34, however, is not affixedto the cylindrical shaft 16, but rather may travel in a reciprocatingmotion about the surface of the shaft 16.

A spring 38 is further provided about the surface of the cylindricalshaft 16 positioned between collars 34 and 36, so that one end of thespring 38 contacts collar 34 while the other end of the spring 38contacts collar 36. Therefore, the motion of collar 34 toward stationarycollar 36 is opposed by the force exerted by spring 38, since the spring38 must be compressed in order for reciprocating collar 34 to movetoward stationary collar 36. The reciprocating motion of the collar 34in the direction away from that of collar 36 is restricted by a movementinhibiting device positioned on the surface of shaft 16. The movementinhibiting device is placed on the opposite side of reciprocating collar34 from stationary collar 36, whereby the force exerted by the spring 38on reciprocating collar 34 presses the collar 34 to abut the movementinhibiting device.

The reciprocating collar 34 is further affixed to the outer sleeve 30,wherein the sleeve 30 extends around the periphery of both collars 34and 36. In the preferred embodiment of the present invention, aplurality of screws 40 extend through apertures 42 in the outer sleeve30 and threadingly engage with reciprocating collar 34 in order tosecure the outer sleeve 30 to the collar 34. However, it is understoodby those skilled in the art that outer sleeve 30 may be affixed toreciprocating collar 34 by any device which securely fastens the outersleeve 30 to the collar 34. Accordingly, the outer sleeve 30 alsoreciprocates, along with collar 34, about the outer surface ofcylindrical shaft 16. When spring 38 is in its normal position forcingreciprocating collar 34 against the movement inhibiting device, theouter sleeve covers both collars 34 and 36 and extends to further coverconnection device 24.

Therefore, in order to secure the vacuum tube assembly 2 to taperedprojection 12, the outer sleeve 30 must be forced toward end 20 of thecylindrical shaft 16 in order to allow access to connection device 24.Enough force must be exerted against the outer sleeve 30, and in turnreciprocating collar 34, to overcome the force being exerted by spring38 resisting compression. Once sufficient force is applied, the spring30 will compress and the outer sleeve will traverse about the outersurface of shaft 16 toward end 20, thus exposing connection device 24.The screws 32 incorporated within connection device 24 may then betightened to frictionally engage tapered projection 12, as illustratedin FIG. 3, to secure the vacuum tube assembly to tapered projection 12.Once the vacuum tube assembly 2 is secured to tapered projection 12, theforce being exerted against outer sleeve 30 to overcome spring 38 isceased, and the spring 38 will force reciprocating collar 34 backtowards end 22 of shaft 16. Thus, outer sleeve 30 will then travel aboutthe surface of shaft 16 away from end 20 until the outer sleeve 30 abutsmounting plate 10. The outer sleeve 30 will come into contact withmounting plate 10 before reciprocating collar 34 contacts the movementinhibiting device, so that the contact between mounting plate 10 andouter sleeve 30 will prevent reciprocating collar 34 from abutting themovement inhibiting device. Once the vacuum tube assembly 2 is attachedto the tapered projection 12 as described above and the outer sleeve 30is abutting mounting plate 10, the process of overlaying a plasticmaterial over the cast 4 and attachment device 6 to thereby form theprosthetic socket is ready to be performed.

Referring now to FIGS. 4 and 5, the process of overlaying the plasticmaterial will be described in greater detail. A sheet of plasticmaterial 44 is first heated into a pliable state. A sheet of reinforcingmaterial 43 can also be added to the sheet of plastic material 44 tostrengthen the component attachment point, wherein the reinforcing sheet43 is preferably metal. The reinforcing sheet 43 is bonded to theplastic sheet 44 by heating the reinforcing sheet 43 to the sametemperature as the heated pliable plastic sheet 44, and then the twosheets 43 and 44 are thermobonded together in an oven or other heatingdevice by lying the reinforcing sheet 43 on top of the heated plasticsheet 44. The heated plastic sheet 44 and reinforcing sheet 43 are thenwrapped around the attachment device 6, a portion of the cast 4, and aportion of the outer sleeve 30. The reinforcing sheet 43 beingpositioned between the plastic sheet 44 and mounting plate 10, foammaterial 14 and cast 4, where the reinforcing sheet 43 extends fromouter sleeve 30 to cast 4 approximately one to three inches abovemounting plate 10. The plastic sheet 44 is wrapped around the fullperimeter of these components until the end of the plastic sheet 44 isjoined with the beginning of the plastic sheet 44, where the two ends ofthe pliable plastic sheet 44 are molded together at 46 to fullyencapsulate the components. Any excess portion of plastic sheet 44extending beyond where the plastic sheet 44 is joined together at 46 maybe cut off, leaving a rib 46. Thereafter, a suction device attached toend 20 of cylindrical shaft 18 is activated to begin a flow of airthrough shaft 16 toward the suction device at end 20. Any air which ispresent underneath of the sheet of plastic material 44, between theplastic material 44 and cast 4, attachment device 6 and sleeve 30, willbe removed and forced between the contacting surfaces of outer sleeve 30and mounting plate 10, through passage 26 in connection device 24,further through central passage 18 and finally to the suction device atthe end 20 of shaft 16. Removing the air underneath of plastic sheet 44effectively shrinks the plastic sheet 44 onto the componentstherebeneath, so that when the heated plastic sheet 44 cools it willresult in an airtight bond between the plastic sheet 44 and thecomponents therebeneath.

In order to increase the strength and effectiveness of the vacuumcreated, two strings 45a and 45b may be tied around the plastic sheet 44after it has been wrapped around the components. A first string 45a istied around the plastic material 44 surrounding the molded cast 4,thereby tightly pressing the plastic sheet 44 against the cast 4 andpreventing the flow of air between plastic sheet 44 and the cast 4underneath of the string 45a. A second string 45b is tied around theplastic material 44 surrounding the sleeve 30, thereby tightly pressingthe plastic sheet 44 against the sleeve 30 and preventing the flow ofair between plastic sheet 44 and the sleeve 30 underneath of the string45b. Therefore, a closed air pocket is formed between the two strings45a and 45b with the only flow of air traveling from the closed airpocket to the suction device through passage 18 in shaft 16. This airpath is achieved because the area between the abutting surfaces of themounting plate 10 and outer sleeve 30 is permeable to air. However, eventhough an air-tight seal is not formed, the outer sleeve 30 is beingforced against mounting plate 10 by spring 38 tightly enough that thereis not sufficient distance between the outer sleeve 30 and the mountingplate 10 to allow the flow of the pliable plastic material therebetween.Therefore, no plastic material 44 comes into contact with the taperedprojection 12 during the plastic overlay procedure.

In addition to increasing the effectiveness of the vacuum, the strings45a and 45b also serve to score the plastic sheet 44 providing abreaking point where the plastic sheet 44 outside of the strings may beremoved. Tying the strings 45a and 45b tightly around the plastic sheet44 makes the pliable plastic sheet 44 thinner beneath the strings 45aand 45b, so that excess plastic material may be easily removed leavingonly the portion of the plastic sheet 44 between the two strings 45a and45b. Since the strings 45a and 45b create the closed air pocket betweenthem, the portion of the plastic sheet 44 outside of the strings 45a and45b will not shrink when the vacuum is applied to the plastic sheet 44.Therefore, the portion of the plastic sheet outside of the strings 45aand 45b can be easily removable. Accordingly, the string 45a wrappedaround cast 4 may be varyingly positioned to provide the desired lengthof the plastic material 44 on each specific prosthetic socket formeddepending upon the support needed. The other string 45b is wrappedaround outer sleeve 30 adjacent to where the outer sleeve 30 abutsmounting plate 10, which allows most of the plastic material 44 on thesleeve 30 side of mounting plate 10 to be easily removed.

Once the vacuum has removed all of the air in the closed air pocket, thestrings 45a and 45b are removed from around the plastic material 44 andthe plastic material 44 is left to cool and harden. Once cooled, theexcess plastic material outside of where the strings 45a and 45b weretied is removed by cutting the thinned plastic material where thestrings 45a and 45b were tied and the excess plastic material isremoved. The vacuum tube assembly 2 is now ready to be removed from thefinished prosthetic socket 50. The outer sleeve 30 is forced toward theend 20 of shaft 16 to allow access to connection device 24, wherein thescrews 28 are loosened to disengage from tapered projection 12. Theformation process for the prosthetic socket 50 is now complete.

Referring now to FIGS. 6 and 7, the completed prosthetic socket 50 willbe described in greater detail. As can be seen from the Figures, thelayer of plastic material 44 conforms to the shape of the cast 4, foammaterial 14 and mounting plate 10. The thickness of the plastic layer 44is most effective within the range of 1/8 inch to 1/2 inch, and in thepreferred embodiment of the present invention should comprise athickness of 3/16 inch. For the average individual wearing thisprosthetic socket 50, it has been found that 3/16 inch provides theoptimal thickness for the plastic layer 44 taking into account certaindesign characteristics, such as strength and weight of the socket 50.For heavier individuals, the thickness of the plastic layer ispreferably 1/4 inch to provide greater strength and stability in theprosthetic socket 50.

It can be further seen from FIG. 6 that mounting plate 10 has both aproximal shoulder 52 and a distal shoulder 54. The proximal shoulder 52is formed by attaching a foam material 14 to the mounting plate 10,wherein the foam material 14 includes a slightly smaller perimeter thanthe mounting plate 10 and the distance between the two perimeterscreates the proximal shoulder 52. The distal shoulder 54 is integrallyformed with the mounting plate 10. It is important that the proximalshoulder 52 is not made to be too large, because the width of proximalshoulder 52 can affect the strength of the plastic layer 44. Since theplastic layer 44 conforms to the shape of the foam material 14 andmounting plate 10, a wide proximal shoulder 52 would cause the plasticlayer 44 to be drawn into the shoulder area. If the plastic layer 44 isdrawn into too deep of a proximal shoulder 52, the plastic layer 44would make a 90° turn around the mounting plate 10 and into proximalshoulder 52. Sharp turns of this sort in the plastic layer 44 cause theplastic to weaken at these points in the layer 44. Therefore, it isimportant to minimize the angles of direction the plastic layer 44 mustturn in order to prevent weak stress points from developing.Accordingly, the foam material 14 must be formed so as not to create adeep proximal shoulder 52 on the mounting plate 10.

A recessed socket 56 is also formed around the distal shoulder on themounting plate 10. Since the outer sleeve 30 abuts the distal shoulder54 of mounting plate 10 during the formation of the plastic layer 44, noportion of the plastic layer 44 is formed on the tapered projection 12.Furthermore, when the excess plastic material is cut from the plasticlayer 44, the cut is made a slight distance below the distal shoulder 54portion of mounting plate 10 so that the plastic layer extends beyondshoulder 54. Additionally, the diameter of the outer sleeve 30 issmaller than the diameter of mounting plate 10, which allows the plasticsheet 44 to be formed on a portion of distal shoulder 54. The portion ofthe plastic sheet 44 extending beyond distal shoulder 54 forms arecessed socket 56 between that portion of the plastic sheet 44 andtapered projection 12. The recessed socket 56, free from plasticmaterial, provides access to tapered projection 12 without having tofirst clean plastic material from the projection 12, wherein taperedprojection 12 is where the prosthetic socket 50 is attached to anartificial limb. Since no plastic material needs to trimmed from thesurface of tapered projection 12, this method of manufacturing aprosthetic socket 50 results a simpler and cleaner way to provide accessto the attachment device 6 of the prosthetic socket 50.

The structure of the preferred embodiment of the present inventionprovides a stronger connection between the attachment device 6 and cast4 than could be achieved in the past. The plastic layer 44 affixing theattachment device 6 to the cast 4 resists any circumferential forcesthat may be exerted on the attachment device 6, because the plasticlayer 44 surrounds the perimeter of both the cast 4 and attachmentdevice 6. Since the layer of plastic 44 extending over cast 4 alsoextends over the proximal shoulder 52 and distal shoulder 54 of mountingplate 10, the plastic layer 44 resists any upward and downward forcesthat may be exerted on the attachment device 6.

Furthermore, the structure of the preferred embodiment provides a morestable connection between the prosthetic socket 50 and an artificiallimb due to the recessed socket 56 formed in the attachment device 6.When the artificial limb connects to tapered projection 12, theartificial limb may receive additional lateral support from the portionof plastic sheet 44 that extends beyond the distal end 54 of mountingplate 10. This added support would provide a more stable connectionbetween the prosthetic socket 50 and artificial limb than the taperedprojection 12 could provide by itself. Additionally, the foam material14 may be removed from the prosthetic socket after molding is completein order to lighten the prosthetic socket 50 without affecting itsstability.

As can be seen by the foregoing, a prosthetic socket formed inaccordance with the present invention will provide an improved method offorming a plastic layer on a cast and an attachment device without theneed for trimming excess plastic from the attachment device. Moreover,by forming a prosthetic socket in accordance with the present invention,a stronger support is provided between the prosthetic socket andartificial limb.

While the present invention has been described with reference to apreferred embodiment, it should be appreciated by those skilled in theart that the invention may be practiced otherwise than as specificallydescribed herein without departing from the spirit and scope of theinvention. Specifically, while the vacuum tube assembly 2 discussedabove included most of its components described as being cylindrical, itis understood that these components, such as shaft 16, sleeve 30,connection device 24 and collars 34 and 36, may comprise any shape whichallows them to function in accordance with the present inventiondiscussed above. It is, therefore, to be understood that the spirit andscope of the invention be limited only by the appended claims.

What is claimed is:
 1. A method for forming a socket for connecting aprosthesis to an amputated extremity, comprising the steps of:forming amolded cast into which the amputated extremity conforms; said moldedcast having a closed distal end and an open proximal end for surroundingthe amputated extremity; forming a vacuum assembly by connecting anattachment means for receiving a vacuum tube to said distal end of saidmolded cast and attaching a first end of said vacuum tube to saidattachment means; wrapping a formable plastic layer around a portion ofsaid vacuum tube, said attachment means and at least said distal end ofsaid molded cast; sealing said plastic layer around said vacuum tube andat least said distal end of said molded cast; drawing air trappedbetween said plastic layer and said vacuum assembly through said vacuumtube; conforming said formable plastic layer to at least said distal endof said molded cast and said attachment means; trimming excess portionsof said formable plastic layer; and removing said vacuum tube leavingsaid attachment means secured in place by said formable plastic layer.2. The method for forming a socket for connecting a prosthesis to anamputated extremity defined in claim 1, wherein said plastic layer is ofthickness in a range of 1/8 inch to 1/2 inch.
 3. The method for forminga socket for connecting a prosthesis to an amputated extremity definedin claim 2, wherein said plastic layer has a thickness of 3/16 inch. 4.The method for forming a socket for connecting a prosthesis to anamputated extremity defined in claim 1, wherein said attachment meansincludes a metal plate having a foam material attached thereto; saidfoam material also being attached to said distal end of said moldedcast.
 5. The method for forming a socket for connecting a prosthesis toan amputated extremity defined in claim 1, wherein the step of trimmingexcess portions of said formable plastic layer from said vacuum tubecomprises the steps of:wrapping a string means around the formableplastic layer; said string means forming score lines in the plasticlayer by thinning the plastic layer underneath the string means; coolingsaid plastic layer; removing said string means; cutting said plasticlayer along said score lines; and removing the excess portions of saidplastic material.
 6. The method for forming a socket for connecting aprosthesis to an amputated extremity defined in claim 1, wherein saidattachment means is recessed within said plastic layer.